Devices for producing sterile saline slush are known in the art. Sterile saline slush is used in a variety of surgical applications to slow organ and tissue metabolic rates thereby protecting organs from irreversible tissue damage during cardiac, neurological organ transplant, vascular, urologic and other complex surgeries. It is important that the slush has as smooth, spherical a configuration as possible to ensure atraumatic slush without sharp crystal edges that could puncture or damage human flesh or organs. The slush should have a substantially uniform consistency to maintain optimal thermodynamic cooling performance.
In both the surgical and non-surgical methods, slush production depends on the same basic thermodynamic phenomena. As ice grows from water that contains “impurities” the water produces a crystal matrix with the “impurities” dispersed into the interstices of the matrix. The term “impurities” are used because of the way they affect the water crystal matrix, however, they are often desirable and necessary components. In the case of non-surgical slush for drinks, the “impurities” are things like sugar and flavor mixes. In the case of surgical slush the “impurity” is salt. The impurities also provide nucleation sites that allow ice crystals to initially form. During the process of freezing a stagnant container of water with impurities, a boundary layer of slush (ice crystal in a fluid mixture) can form between a solid ice layer and a liquid water layer.
If during the freezing process the fluid mixture is mechanically agitated, small crystal formations are generated at the nucleation sites but size growth of the crystal matrix is inhibited because mechanical agitation prevents larger crystal growth. When these small crystals are suspended in the bulk fluid they form a slurry or slush. Mechanical agitation also helps keep the bulk fluid temperature more consistent and helps reduced large crystal growth that would otherwise occur at the fluid boundary (i.e. surface or container walls) where heat is typically being transferred out of the fluid.
In some prior art devices fluid is contained in a basin lined with a drape. Mechanical agitation of the fluid is provided by continually flexing the drape by lifting the drape from below with a pin or arm. The top of the basin is open to ambient air and the fluid is cooled via the metal walls and bottom that supports the drape. With this arrangement, flexing of the drape is essential to prevent large crystal formation in the fluid that is contact with the drape where heat is being transferred away from the fluid. The drape flexing also needs to be sufficient to keep the bulk mixture consistent and to keep the crystal suspended in the slush mixture. However, the need for aggressive mixing needs to be balanced with the need to maintain the integrity of the drape boundary because the drape also serves as a sterile barrier.
The integrity of the sterile field is very important during surgery. Any breach that might indicate that the sterile field has become contaminated is taken very seriously. A breach that is undiscovered for a period of time is especially troublesome as it is difficult to assess when the breach was created and whether it caused the patient to be exposed to contaminants while vulnerable during surgery. Thus it is no wonder that there may be grave concerns about the ongoing potential for breaches in the sterile field maintained by sterile drapes.
Other methods of creating slush had other shortcomings. One such method called for placing bags of sterile saline in freezers to freeze the sterile saline solution and then smashing the bag with a mallet to create slush. Such a method has a number of shortcomings including the risk of forming jagged ice crystals.
Another method called for the use of a frozen metal basin and chilled alcohol. This method involved pouring sterile saline inside the basin and scraping the side of the basin until sufficient slush is collected. The method produces slush, but is time consuming and resource intensive. Such a process does not scale well to provide a device that creates and maintains a significant amount sterile surgical slush.